(1) Field of the Invention
The present invention relates to an apparatus and method of metering a low pressure fluid into a high pressure fluid flow. The fluids include gases, liquids, flowable solids, slurries, etc. In particular, the present invention relates to a fluid dispensing system that employs a peristaltic pump to dispense an accurate, continuous flow of a first fluid at a first pressure into a fluid conduit conducting a second fluid at a second pressure greater than the pressure of the first fluid. A pressure reducer assembly is inserted in the fluid conduit to reduce the pressure of the second fluid to a pressure below the pressure of the first fluid by increasing the flow velocity of the second fluid, thereby enabling the peristaltic pump to pump the first fluid at the first pressure into the fluid conduit. A pressure relief valve is provided in the feed line between the peristaltic pump and the pressure reducer to prevent the creation of a vacuum pressure in the feed line which could interfere with the proper operation of the pump.
(2) Description of the Related Art
In fluid mixing systems of the prior art, it is often necessary to mix a first fluid with a second fluid being carried by a fluid conduit, where only a very small amount of the first fluid is desired to be combined with a much greater amount of the second fluid. For example, it is often necessary to feed very small amounts of a first fluid, in the order of 5.0.times.10.sup.-4 gallons per minute, at an accurate and continuous rate of feed into a conduit conducting a second fluid at a much greater pressure than the first fluid. It is also necessary to provide such a fluid mixing system that is inexpensive to construct and operate, and will operate reliably for a period of five to ten years.
Previous efforts in the prior art to provide such a fluid mixing system have employed small diaphragm or piston pumps, suction devices such as orifices, and mechanical syringe fluid dispensers. However, these prior art systems are typically incapable of providing the desired continuous and accurately metered flow rate of the first fluid into the conduit conducting the second fluid.
Peristaltic pumps or tube pumps are capable of delivering a continuous and accurately metered low flow rate of fluid. However, peristaltic pumps are typically limited to low pressure head applications (20 psig to 70 psig maximum). When connecting a first fluid line carrying fluid pumped at a low flow rate and low pressure by a peristaltic pump, to a second fluid line conducting a second fluid at a much higher pressure, the high pressure of the second fluid carried in the second line will in most cases cause the first fluid pumped by the peristaltic pump in the first fluid line to back up and increase in pressure until the pressure of the first fluid prevents the peristaltic pump from working properly. The increase in pressure of the first fluid could possibly reach a level that prevents the peristaltic pump from rotating and the increase in the pressure level could burst an output hose or conduit of the pump, or the pump tube itself. The increase in pressure could also cause the fluid to be backed up through the pump or cause the pump to run backward and damage the pump motor.
What is needed to overcome these disadvantages of prior art fluid mixing systems is an apparatus and method of dispensing a continuous, accurately metered flow of a first fluid at a low pressure, into a flow of a second fluid conducted by a fluid conduit where the second fluid has a much higher pressure. Such a fluid mixing system must be inexpensive to construct and operate, and must operate reliably over a period of five to ten years to be practical.